The influence of western spruce budworm on fire in spruce-fir forests

Western spruce budworm (Choristoneura freemani Razowski; WSBW) is the most significant defoliator of coniferous trees in the western United States. Despite its important influence on Western forests, there are still gaps in our knowledge of WSBW’s impact on fire, and little research has been done on this relationship in high-elevation spruce-fir forests. Although this species is native to western North America, current outbreaks have persisted for many years in some areas, leading to high mortality rates among host tree species. Using the Fire and Fuels Extension of the Forest Vegetation Simulator (FFE-FVS), we examined the current and future impact of an ongoing WSBW outbreak on potential fire behavior in spruce-fir forests in northern New Mexico, USA. We found that this ongoing WSBW outbreak resulted in little to no difference in fire behavior under moderate fire weather conditions. Under high-severity fire weather conditions, stands enduring WSBW outbreaks experienced less severe fire behavior. We also found that WSBW outbreaks resulted in a decrease in fire behavior under severe fire weather conditions for 40 years following the outbreak.